Everton have been dealt a serious setback on the eve of the new Premier League season after Ross Barkley suffered a training ground injury that could sideline the England international for up to two months.

The 20-year-old damaged his knee on Friday during preparations for the campaign’s opener against Leicester City and left the club’s Finch Farm training ground wearing a protective brace. The full extent of the injury will not be known until Barkley undergoes a scan on the problem on Saturday, although the initial concern at Everton is that their influential midfielder will be absent for between six and eight weeks.

Such a lengthy lay-off would be a major blow for Everton manager Roberto Martínez and would also impact on England’s European Championship qualifiers. Roy Hodgson’s team have a friendly against Norway on 3 September, their opening qualifier against Switzerland five days later and a qualifying double-header against San Marino and Estonia on 9 and 12 October respectively. Barkley would only be scheduled to return from injury in mid-October, should he be sidelined for eight weeks.

The midfielder signed a new four-year, £60,000-a-week contract with Everton last month as the club rewarded his impressive emergence last season and secured his services long term.

Unless the scan reveals unexpectedly positive news, Barkley is set to miss league games against Leicester, Arsenal, Chelsea, West Bromwich Albion, Crystal Palace, Liverpool and possibly Manchester United, plus the start of Everton’s involvement in the Europa League and Capital One Cup.